Device and method for surface machining a workpiece

ABSTRACT

The invention relates to an apparatus and a method for surface machining. The apparatus for surface machining a workpiece, i.e., for abrasive flow machining, has at least two opposite pressure devices, such that the workpiece to be machined is arranged between the opposite pressure devices and an abrasive can be moved past the workpiece to be machined. According to the invention, the opposite pressure devices can be pressurized with a defined pressure to establish a uniform pressure in the entire abrasive on every side of the workpiece to be machined. The movement of the abrasive relative to the workpiece to be machined is adjustable by a movement of the pressure devices in the same direction while maintaining the uniform pressure.

This application claims the priority of International Application No. PCT/DE2004/000106, filed Jan. 24, 2004, and German Patent Document No. 103 09 456.3, filed Mar. 5, 2003, the disclosures of which are expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to an apparatus for surface machining a workpiece. The invention further relates to a method for surface machining a workpiece.

In the surface treatment of workpieces a distinction is drawn between chip removal processes and nontraditional material removal processes. Chip removal processes use the mechanical action of cutters on the workpiece and thereby cause material to be removed from the workpiece surface being machined. Nontraditional material removal processes use chemical or thermal processes for the surface treatment.

The chip removal processes include so-called lapping. The cutter used in lapping is an abrasive that consists of abrasive grains and a carrier medium. In lapping, the surface of the workpiece to be machined is treated by means of the abrasive grains loosely distributed in the carrier medium, such that the abrasive grains are guided in random cutting paths relative to the workpiece to be machined.

A special form of lapping is abrasive flow machining or AFM. In abrasive flow machining the workpiece to be machined is usually clamped between two opposite, vertically disposed pressure pistons or pressure cylinders. The abrasive is pushed back and forth between the two pressure pistons or pressure cylinders by lifting and lowering the pressure pistons and is thereby guided past the workpiece surface to be machined. The removal of material from the surface being machined is determined by various process parameters, such as the pressure of the abrasive, temperature of the abrasive and viscosity or flow behavior of the abrasive. The greatest removal of material occurs in the region with the highest flow resistance. The present invention relates to abrasive flow machining.

The prior art methods for surface machining a workpiece relating to abrasive flow machining has the drawback that the work results that can be achieved are inconsistent. This is due, in particular, to the large number and inconsistency of the process parameters responsible for the removal of material. Particularly if the workpiece to be machined has curved surfaces, there are substantial differences in the removal of material along the surfaces being machined, depending on whether the surface is facing toward or away from the flow direction or moving direction of the abrasive. Further irregularities in the removal of material according to the prior art result because the abrasive becomes hot with increasing machining time and the viscosity or flow rate of the abrasive changes as a result.

Based thereon, it is an object of the present invention to provide a novel apparatus for surface machining a workpiece and a corresponding method.

The apparatus has at least two opposite pressure devices, such that the workpiece to be machined is arranged between the opposite pressure devices and an abrasive can be moved past the workpiece to be machined. According to the invention, the opposite pressure devices are pressurized with a defined pressure, such that a uniform pressure is established in the entire abrasive on every side of the workpiece to be machined. The movement of the abrasive relative to the workpiece to be machined can be adjusted by a movement of the opposite pressure devices in the same direction while maintaining the uniform pressure in the abrasive. The uniform pressure on all sides of the workpiece to be machined causes a uniform removal of material on all sides of the workpiece. The machining of the surface is thereby improved.

According to an advantageous further refinement of the invention, the apparatus has two opposite pressure devices, between which the workpiece is clamped by means of a mechanism. The first, upper pressure device is mounted to a first horizontally extending cross member and another, lower pressure device to a second horizontally extending cross member. The two cross members are interconnected. The two pressure devices can be displaced relative to the mechanism by a vertical movement of the two cross members. This vertical movement of the two cross members can be used to adjust the movement of the abrasive relative to the workpiece to be machined.

Preferably, the or each cross member is a controllable drive unit for ensuring a uniform flow rate of the abrasive relative to the workpiece to be machined. By maintaining a constant flow rate of the abrasive, it is possible to improve the surface machining result.

According to another advantageous further refinement of the invention, a controllable cooling and/or heating device for the abrasive is provided to ensure a uniform temperature of the abrasive. By maintaining a constant temperature of the abrasive, the surface machining result can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention, which shall not be construed as a limitation thereof, will now be described with reference to the drawings, in which:

FIG. 1: is a highly schematic representation of an apparatus for surface machining a workpiece according to the prior art,

FIG. 2: is a highly schematic representation of the apparatus for surface machining a workpiece according to the invention, and

FIG. 3: is an enlarged detail of the arrangement shown in FIG. 2 with additional guide elements.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a highly schematic representation of the apparatus 10 for abrasive flow machining according to the prior art. In the prior art apparatus 10, two pressure cylinders 11, 12 are disposed vertically one above the other. A workpiece 13 to be machined is clamped between these two pressure cylinders 11, 12. In the arrangement depicted in FIG. 1, the workpiece 13 has a borehole, the inner surface of which is to be machined. To this end, an abrasive 14 is pushed back and forth between the pressure cylinders 11, 12, which are arranged vertically one above the other. The movement of the abrasive 14 is effected by the pressure pistons 15, 16 associated with the pressure cylinders 11, 12.

FIG. 2 shows an apparatus 17 for abrasive flow machining according to the invention. The inventive apparatus 17 has two opposite pressure devices 18, 19, i.e., a first upper pressure device 18 and a second lower pressure device 19. The two pressure devices 18, 19 are designed as cylinder-piston systems.

A workpiece to be machined 21 is positioned and clamped between the two pressure devices 18, 19 by means of a mechanism 20. In the exemplary embodiment shown in FIG. 2, the workpiece 21 is a gas turbine assembly. FIG. 2 shows three blades 22 of this gas turbine assembly.

According to FIG. 2, the first upper pressure device 18 is connected to a first horizontally extending cross member 23. The second lower pressure device 19 is connected to a second, likewise horizontally extending cross member 24. The two horizontally extending cross members 23, 24 are interconnected at opposite ends by vertically extending supports 25, 26. The two pressure devices 18, 19 can be pressurized with a defined pressure, such that a uniform pressure is established in the entire abrasive and thus on every side of the workpiece to be machined 21 or the blades to be machined 22. By moving the entire unit which consists of the cross members 23 and 24, the supports 25 an 26 and the pressure devices 18 and 19 connected to the cross members 23, 24 relative to the mechanism 20, the movement of the abrasive 27 in relation to the workpiece to be machined 21, or the blades to be machined 22, can be adjusted while maintaining the uniform pressure of the abrasive. This makes it possible to achieve a uniform removal of material along the surfaces of the workpiece 21, even if the surfaces of the workpiece to be machined 21 are curved.

The cross members 23, 24 and the supports 25, 26 are associated with a controllable drive unit. The drive unit is used to realize the movement of the unit which consists of the cross members 23 and 24, the supports 25 and 26 and the pressure devices 18 and 19 connected to the cross members 23, 24 relative to the mechanism 20. This controllable drive unit makes it possible to adjust a uniform flow rate of the abrasive 27 relative to the workpiece to be machined 21.

A further characteristic of the invention is that the apparatus 17 has a controllable cooling and/or heating device (not depicted) for the abrasive 27. This cooling and/or heating device for the abrasive 27 is used to adjust a uniform temperature for the abrasive 27.

The apparatus according to the invention thus makes it possible to uniformly adjust or control the process parameters to a constant value, i.e., the pressure of the abrasive, the flow rate of the abrasive and the temperature of the abrasive. This in turn makes it possible for the first time to obtain reproducible surface machining results using the so-called abrasive flow machining technique. The uniform pressure of the abrasive ensures uniform machining of every point of the workpiece surface to be machined, even if the surfaces of the workpiece are curved.

FIG. 3 shows a further refinement of the invention. In the arrangement illustrated in FIG. 3, guide elements 28 are disposed in the region of the workpiece to be machined 21, or the blades to be machined 22. These guide elements 28 are used to influence both the moving direction and the flow rate of the abrasive 27. This makes it possible to locally influence the removal of material along the surface to be machined.

The method according to the invention is carried out using the apparatus according to the invention as described with reference to FIG. 2 and 3. In the method according to the invention, the abrasive 27 is guided past the workpiece to be machined 21, such that a uniform pressure is established in the entire abrasive 27 and thus relative to every side of the workpiece to be machined 21. The abrasive 27 is moved in relation to the workpiece to be machined 21 while maintaining this uniform pressure. The flow rate and temperature of the abrasive can be controlled to constant values. The guide elements 28 are used to influence a moving direction and/or the flow rate of the abrasive.

The apparatus and method according to the invention are particularly suitable to surface machine complex three-dimensional geometries, particularly to machine blisks of a gas turbine.

LIST OF REFERENCE NUMBERS

apparatus 10 pressure cylinder 11 pressure cylinder 12 workpiece 13 abrasive 14 pressure piston 15 pressure piston 16 apparatus 17 pressure device 18 pressure device 19 mechanism 20 workpiece 21 blade 22 cross member 23 cross member 24 support 25 support 26 abrasive 27 guide element 28 

1-12. (canceled)
 13. An apparatus for surface machining a workpiece for abrasive flow machining, having at least two opposite pressure devices, wherein the workpiece to be machined is arranged between the opposite pressure devices, and wherein an abrasive is moved past the workpiece to be machined, wherein the opposite pressure devices are pressurized with a defined pressure, a uniform pressure is established in an entirety of the abrasive on every side of the workpiece to be machined, and the movement of the abrasive relative to the workpiece to be machined is adjusted by a movement of the pressure devices in a same direction while maintaining the uniform pressure.
 14. The apparatus as claimed in claim 13, wherein the workpiece to be machined is clamped between the opposite pressure devices by means of a mechanism.
 15. The apparatus as claimed in claim 13, wherein the pressure devices are mounted to at least one cross member, and the movement of the abrasive relative to the workpiece to be machined is adjusted by a movement of each cross member.
 16. The apparatus as claimed in claim 13, wherein the two opposite pressure devices, between which the workpiece to be machined is clamped by means of a mechanism, include a first upper pressure device mounted to a first horizontally extending cross member and a second lower pressure device mounted to a second horizontally extending cross member.
 17. The apparatus as claimed in claim 16, wherein the two cross members are interconnected and the two pressure devices are displaceable by a vertical movement of the two cross members relative to the mechanism, such that this vertical movement of the two cross members is used to adjust the movement of the abrasive relative to the workpiece to be machined.
 18. The apparatus as claimed in claim 13, wherein each cross member is assigned a controllable drive unit to ensure a uniform flow rate of the abrasive relative to the workpiece to be machined.
 19. The apparatus as claimed in claim 13, further comprising a controllable cooling and/or heating device for the abrasive to ensure a uniform temperature of the abrasive.
 20. The apparatus as claimed in claim 13, further comprising at least one guide element positioned in a region of the workpiece to be machined to influence the moving direction and/or flow rate of the abrasive.
 21. A method for surface machining a workpiece for abrasive flow machining, wherein an abrasive is moved past the workpiece to be machined, wherein opposite pressure devices are used to establish a uniform pressure in an entirety of the abrasive on every side of the workpiece to be machined, and the abrasive is displaced relative to the workpiece to be machined by a movement of the opposite pressure devices while maintaining the uniform pressure.
 22. The method as claimed in claim 21, wherein a flow rate of the abrasive relative to the workpiece to be machined is controlled to a constant value.
 23. The method as claimed in claim 21, wherein a temperature of the abrasive is controlled to a constant value.
 24. The method as claimed in claim 21, wherein a moving direction and/or flow rate of the abrasive is influenced.
 25. A device for surface machining a workpiece for abrasive flow machining, comprising: first and second opposite pressure devices adapted to receive the workpiece therebetween, the opposite pressure devices positioned to allow an abrasive to be moved past the workpiece, wherein a uniform pressure in the abrasive on each side of the workpiece is established, and wherein a movement of the abrasive relative to the workpiece is adjustable by moving the opposite pressure devices in a same direction while maintaining the uniform pressure.
 26. The device of claim 25, further comprising a clamping mechanism for holding the workpiece between the opposite pressure devices.
 27. The device of claim 25, further comprising a cross member mounted to at least one of the pressure devices, wherein the movement of the abrasive relative to the workpiece is adjustable by a movement of the cross member.
 28. The device of claim 25, wherein the first pressure device is mounted to a first horizontally extending cross member and the second pressure device is mounted to a second horizontally extending cross member.
 29. The device of claim 28, wherein the two cross members are interconnected, and wherein a vertical movement of the two cross members relative to the mechanism adjusts the movement of the abrasive relative to the workpiece.
 30. The device of claim 25, further comprising first and second controllable drive units, assigned to the first and second cross members, respectively, the controllable drive units operable to ensure a uniform flow rate of the abrasive relative to the workpiece.
 31. The device of claim 25, further comprising a controllable temperature device to maintain the abrasive at a uniform temperature.
 32. A method for surface machining a workpiece for abrasive flow machining, comprising the steps of: moving an abrasive past the workpiece; using opposite pressure devices to establish a uniform pressure in the abrasive on every side of the workpiece, and displacing the abrasive relative to the workpiece by moving the opposite pressure devices while maintaining the uniform pressure.
 33. The method of claim 32, further comprising controlling at a constant rate a flow rate of the abrasive relative to the workpiece.
 34. The method of claim 32, further comprising controlling at a constant value a temperature of the abrasive.
 35. The method of claim 32, wherein a moving direction of the abrasive is influenced.
 36. The method of claim 32 wherein a flow rate of the abrasive is influenced. 